Conformal strippable carbon film for line-edge-roughness reduction for advanced patterning

ABSTRACT

Embodiments of the disclosure relate to deposition of a conformal organic material over a feature formed in a photoresist or a hardmask, to decrease the critical dimensions and line edge roughness. In various embodiments, an ultra-conformal carbon-based material is deposited over features formed in a high-resolution photoresist. The conformal organic layer formed over the photoresist thus reduces both the critical dimensions and the line edge roughness of the features.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 15/137,486, filed onApr. 25, 2016, now issued as U.S. Pat. No. 9,659,771, which claimsbenefit of U.S. provisional patent application Ser. No. 62/174,248,filed Jun. 11, 2015, which is herein incorporated by reference.

BACKGROUND

Field

Embodiments of the present disclosure generally relate to thefabrication of integrated circuits and particularly to methods forchanging critical dimensions of features during an etching process.

Description of the Related Art

Reducing the size of integrated circuits (ICs) results in improvedperformance, increased capacity and/or reduced cost. Each size reductionrequires more sophisticated techniques to form the ICs. Photolithographyis commonly used to pattern ICs on a substrate. An exemplary feature ofan IC is a line of a material which may be a metal, semiconductor orinsulator. Line width is the width of the line and the spacing is thedistance between adjacent lines. Pitch is defined as the distancebetween a same point on two adjacent lines. The pitch is equal to thesum of the line width and the spacing. However, due to factors such asoptics and light or radiation wavelength, photolithography techniqueshave a minimum pitch below which a particular photolithographictechnique may not reliably form features. Thus, the minimum pitch of aphotolithographic technique can limit feature size reduction. Similarly,patterning tools designed to create vias or line interconnects 100 nmwide or more are not commonly able to create smaller vias. Therefore, asdevices shrink to these small dimensions, current lithography processesare challenged to create patterns with the chosen critical dimensions(CD).

Variations in the width of an IC feature along one edge is typicallycalled line-edge roughness (LER). LER has increasingly become a concernin advanced technology nodes, such as for feature sizes on the order of100 nm or less. In one example, when considering LER below 14 nmtechnology node, uncontrolled LER can lead to leaky transistor failurein Front-End-Of-line (FEOL) applications, or reliability loss at theinterconnect level in Back-End-Of-Line (BEOL) applications. Current LERis close to 4-5 nm for both Immersion lithography, and EUV lithography.

One approach to reduce LER is by photoresist curing using implant ore-Beam. However, these approaches decrease throughput and are not costeffective. Further, the photoresist curing methods recited above do notprovide Critical Dimension (CD) shrink. CD shrink is required either toextend current Immersion lithography flow, or to help get narrowerdimension with EUV.

Given the current state of the art, there is a continuing need forreduced CD and LER reduction for advanced technology node applications.

SUMMARY

Embodiments disclosed herein generally relate to methods and apparatusfor decreasing the critical dimensions of a feature formed in aphotoresist or a hardmask. In one embodiment, a method of processing asubstrate includes forming a feature in a photoresist layer to expose aportion of a hardmask layer deposited below the photoresist layer,depositing a first organic layer directly on the photoresist layer, thefirst organic layer conformally covering exposed surfaces of the featureand exposed portions of the hardmask layer, selectively removing thefirst organic layer from a top surface of the photoresist layer and theexposed portions of the hardmask layer, while leaving the first organiclayer deposited on sidewalls of the feature substantially intact,forming a second organic layer conformally on the top surface of thephotoresist layer, the exposed portion of the hardmask layer and thesidewalls of the feature, selectively removing the second organic layerfrom the top surface of the photoresist layer and the exposed portion ofthe hardmask layer, while leaving the second organic layer deposited onthe first organic layer on the sidewalls of the feature substantiallyintact, and forming a pattern into the hardmask layer using thephotoresist layer, the first organic layer and the second organic layeras a mask.

In another implementation, the method includes forming a feature in aphotoresist layer to expose a portion of a hardmask layer depositedbelow the photoresist layer, depositing a first organic layer directlyon the photoresist layer by exposing the photoresist layer to a plasmaformed from a hydrocarbon source, a plasma-initiating gas, and adilution gas, the first organic layer conformally covering exposedsurfaces of the feature and exposed portions of the hardmask layer,selectively removing the first organic layer from a top surface of thephotoresist layer and the exposed portions of the hardmask layer, whileleaving the first organic layer deposited on sidewalls of the featuresubstantially intact, forming a second organic layer conformally on thetop surface of the photoresist layer, the exposed portion of thehardmask layer and the sidewalls of the feature, selectively removingthe second organic layer from the top surface of the photoresist layerand the exposed portion of the hardmask layer, while leaving the secondorganic layer deposited on the first organic layer on the sidewalls ofthe feature substantially intact, and forming a pattern into thehardmask layer using the photoresist layer, the first organic layer andthe second organic layer as a mask.

In yet another embodiment, the method includes forming a feature in aphotoresist layer to expose a portion of a hardmask layer depositedbelow the photoresist layer, depositing a first organic layer directlyon the photoresist layer, wherein the first organic layer is anamorphous carbon layer conformally covering exposed surfaces of thefeature and exposed portions of the hardmask layer, selectively removingthe first organic layer from a top surface of the photoresist layer andthe exposed portions of the hardmask layer, while leaving the firstorganic layer deposited on sidewalls of the feature substantiallyintact, forming a second organic layer conformally on the top surface ofthe photoresist layer, wherein the second organic layer is an amorphouscarbon layer, selectively removing the second organic layer from the topsurface of the photoresist layer and the exposed portion of the hardmasklayer, while leaving the second organic layer deposited on the firstorganic layer on the sidewalls of the feature substantially intact, andforming a pattern into the hardmask layer using the photoresist layer,the first organic layer and the second organic layer as a mask.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above recited features can be understoodin detail, a more particular description of the methods and devices,briefly summarized above, may be had by reference to embodiments, someof which are illustrated in the appended drawings. It is to be noted,however, that the appended drawings illustrate only typical embodimentsand are therefore not to be considered limiting of its scope, for themethods and devices may admit to other equally effective embodiments.

FIG. 1 is a flowchart depicting steps associated with an exemplarypatterning method according to one embodiment of the disclosure.

FIGS. 2A-2H illustrate cross-sectional views representing a patterningmethod as set forth by FIG. 1, according to an embodiment of thedisclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially utilized on other embodiments withoutspecific recitation.

DETAILED DESCRIPTION

Embodiments described herein relate to deposition of an ultra-conformalcarbon-based material for decreasing the critical dimensions and lineedge roughness of a feature formed in a photoresist or a hardmask. Invarious embodiments, an ultra-conformal carbon-based material isdeposited over features formed in a high-resolution photoresist. In oneexample, a low temperature conformal strippable organic layer (referredto herein as the “conformal organic layer”) may be deposited directly onphotoresist. The term “low temperature” described in this disclosure mayrefer to a temperature range of about 150° C. to about 600° C., forexample about 300° C. to about 500° C., such as about 450° C. Thephotoresist will have features formed therein prior to the deposition.The conformal organic layer formed over the photoresist thus reducesboth the CD of the features and the LER of the features, by smoothingedge non-uniformities in the walls of the feature. The conformal organiclayer has the advantage of reacting to the same oxygen chemistry that isused to remove the photoresist layer. Thus, the conformal organic layercan be stripped away in dry oxygen based plasma at the same time asphotoresist strip. This conformal organic layer/photoresist combinationstrip saves one process step, thus reducing costs. Further, being ableto be stripped in dry plasma overcomes the wet strip issues, such aslines collapse (e.g., by capillary effect), and overcomes wet stripinduced defects.

Embodiments described herein may be performed using any suitableprocessing chamber such as a plasma enhanced chemical vapor deposition(PECVD) chamber. The processing chamber may be incorporated into asubstrate processing system. Examples of suitable systems include theCENTURA® systems which may use a DxZ™ processing chamber, PRECISION5000® systems, PRODUCER™ systems, PRODUCER GT™ and the PRODUCER SE™processing chambers which are commercially available from AppliedMaterials, Inc., located in Santa Clara, Calif. It is contemplated thatother deposition processing system, including those available from othermanufacturers, may be adapted to practice the embodiments describedherein.

FIG. 1 is a flow diagram illustrating a method 100 of processing asubstrate, according to one embodiment. FIGS. 2A-2H depictcross-sectional views representing the patterning process as describedin FIG. 1. The method 100 can include forming a pattern in a photoresistlayer on a hardmask layer, the pattern forming one or more featureswhich expose an exposed portion of the hardmask layer, at 102;depositing a conformal organic layer on the photoresist layer, at 104;removing the conformal organic layer from the bottom portion by an etchprocess to expose the exposed portion of the hardmask layer, at 106;etching the exposed portion of the hardmask layer to form a recess inthe hardmask layer, at 108; and removing the remaining portions of theconformal organic layer and patterned photoresist layer simultaneouslyby a plasma ashing method, at 110.

FIG. 2A illustrates a number of possible layers comprising themultilayer substrate 200. Shown here, the multilayer substrate 200includes a substrate 216, an active layer 214, an oxide layer 212, ametal layer 210, a carbon layer 208, an anti-reflective layer 206, ahardmask layer 204 and a photoresist layer 202.

In some embodiments, the multilayer substrate 200 may also include aplurality of alternating oxide and nitride materials (i.e.,oxide-nitride-oxide (ONO), one or more oxide or nitride materials,polysilicon or amorphous silicon materials, oxides alternating withamorphous silicon, oxides alternating with polysilicon, undoped siliconalternating with doped silicon, undoped polysilicon alternating withdoped polysilicon, or undoped amorphous silicon alternating with dopedamorphous silicon deposited on a surface of the substrate. Themultilayer substrate 200 may be a layer stack comprising one or more ofthe following: crystalline silicon, silicon oxide, silicon oxynitride,silicon nitride, strained silicon, silicon germanium, tungsten, titaniumnitride, doped or undoped polysilicon, doped or undoped silicon wafersand patterned or non-patterned wafers, silicon on insulator (SOI),carbon doped silicon oxides, silicon nitrides, doped silicon, germanium,gallium arsenide, glass, sapphire, low k dielectrics, and combinationsthereof. Multilayer substrate 200 may also comprise of layers containingcarbonaceous materials such as photoresists, anti-reflective coatings,and other spin-on coatings.

The method 100 begins at 102 by forming a pattern in a photoresist layeron a hardmask layer, the pattern forming one or more features whichexpose an exposed portion of the hardmask layer. The multilayersubstrate 200 is provided to a plasma processing chamber, wherein themultilayer substrate 200 resides on a temperature controlled substrateholder or chuck. The multilayer substrate 200 is then equilibrated to atemperature less than the decomposition temperature of the photoresistlayer 202. The photoresist layer 202 is disposed over the hardmask layer204 and is patterned using a lithography type process, at 102.

The photoresist layer 202 may be a polymer material sensitive to acertain wavelength of electromagnetic radiation, and may be appliedthrough a spin coating process or a CVD process. In some embodiments,the photoresist layer 202 is a carbon-based polymer sensitive toultraviolet light, such as a phenolic resin, an epoxy resin, or thelike. The photoresist layer 202 may be a positive or a negativephotoresist. Positive photoresists may be selected from the groupconsisting of a 248 nm photoresist, a 193 nm photoresist, a 157 nmphotoresist, and a phenolic resin matrix with a diazonapthoquinonesensitizer. Negative photoresists may be selected from the groupconsisting of poly-cis-isoprene and poly-vinylcinnamate. Notably,photoresist materials will decompose at temperatures much lower than theother non-carbonaceous layers present in the multilayer substrate 200.Photoresist used in embodiments described herein have decompositiontemperatures which range from 100° C. to 150° C. Photoresistdecomposition results in compromised patterning performance and poorprocess yield.

As illustrated by FIG. 2C, conformal organic layer 218 is deposited overthe field region, sidewalls, and the bottom portion formed by thepatterned photoresist layer 202 and the upper surface of the reduceddimension pattern transfer hardmask layer 204, at 104. The conformalorganic layer 218 may be disposed over the patterned photoresist layer202 by a PECVD process from gaseous precursors that are provided to areactor containing the multilayer substrate 200.

Embodiments of the present disclosure may be performed using anysuitable processing chamber such as plasma enhanced chemical vapordeposition chamber. The processing chamber may be incorporated into asubstrate processing system with a temperature controlled chuck to holdthe multilayer substrate 200. Examples of suitable systems include theCENTURA® systems which may use a DxZ™ processing chamber, PRECISION5000® systems, PRODUCER™ systems, PRODUCER GT™ and the PRODUCER SE™processing chambers which are commercially available from AppliedMaterials, Inc., Santa Clara, Calif. It is contemplated that otherprocessing systems, including those available from other manufacturers,may be adapted to practice the embodiments described herein.

The conformal organic layer 218, when deposited using process conditionsdiscussed below, will achieve step coverage of at least about 80% ormore, for example about 100% or more, such as 120%. The thickness of theconformal organic layer 218 may be between about 5 Å and about 200 Å. Inone embodiment, the conformal organic layer 218 is an amorphous carbon(a-C) layer. The amorphous carbon may be undoped or doped with nitrogen.In one example, the conformal organic layer 218 is a nitrogen-dopedamorphous carbon layer. The nitrogen-doped amorphous carbon layer may bedeposited by any suitable deposition techniques such as plasma enhancedchemical vapor deposition (PECVD) process. In one embodiment, thenitrogen-doped amorphous carbon layer may be deposited by flowing, amongothers, a hydrocarbon source, a nitrogen-containing gas such as N₂ orNH₃, a plasma-initiating gas, and a dilution gas into a PECVD chamber.In another embodiment, the nitrogen-doped amorphous carbon layer may bedeposited by flowing, among others, a hydrocarbon source, anitrogen-containing hydrocarbon source, a plasma-initiating gas, and adilution gas into a PECVD chamber. In yet another embodiment, anitrogen-containing hydrocarbon source, a plasma-initiating gas, and adilution gas are flowed into the PECVD chamber to form thenitrogen-doped amorphous carbon protective layer on the patternedfeatures and the exposed surfaces of the substrate 200.

The hydrocarbon source may be a mixture of one or more hydrocarboncompounds. The hydrocarbon source may include a gas-phase hydrocarboncompound and/or a gas mixture including vapors of a liquid-phasehydrocarbon compound and a carrier gas, as will be further discussedbelow. The plasma-initiating gas may be helium since it is easilyionized; however, other gases, such as argon, may also be used. Thedilution gas may be an easily ionized, relatively massive, andchemically inert gas such as argon, krypton, xenon. In some cases,additional hydrogen dilution can be introduced to further increase thefilm density, as will be discussed later.

The hydrocarbon compounds may be partially or completely dopedderivatives of hydrocarbon compounds, including fluorine-containing,oxygen-containing, hydroxyl group-containing, and boron-containingderivatives of hydrocarbon compounds. The hydrocarbon compounds maycontain nitrogen or be deposited with a nitrogen-containing gas, such asammonia, or the hydrocarbon compounds may have substituents such asfluorine and oxygen. Generally, hydrocarbon compounds or derivativesthereof that may be included in the hydrocarbon source may be describedby the formula C_(x)H_(y), where x has a range of between 1 and 20, andy has a range of between 1 and 20. In another embodiment, thehydrocarbon compounds or derivatives thereof that may be included in thehydrocarbon source may be described by the formula C_(x)H_(y)F_(z),where x has a range of between 1 and 24, y has a range of between 1 and50, and z has a range of 0 to 50, and the ratio of x to y+c is 1:2 orgreater. In yet another embodiment, the hydrocarbon source may bedescribed by the formula C_(a)H_(b)O_(c)F_(d)N_(e) for oxygen and/ornitrogen substituted compounds, where a has a range of between 1 and 24,b has a range of between 1 and 50, c has a range of 1 to 10, d has arange of 0 to 50, e has a range of 0 to 10, and the ratio of a tob+c+d+e is 1:2 or greater.

Suitable hydrocarbon compounds include one or more of the followingcompounds, for example, alkanes such as methane (CH₄), ethane (C₂H₆),propane (C₃H₈), butane (C₄H₁₀) and its isomer isobutane, pentane (C₅H₁₂)and its isomers isopentane and neopentane, hexane (C₆H₁₄) and itsisomers 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, and2,2-dimethyl butane, and so on. Additional suitable hydrocarbons mayinclude alkenes such as ethylene, propylene, butylene and its isomers,pentene and its isomers, and the like, dienes such as butadiene,isoprene, pentadiene, hexadiene and the like, and halogenated alkenesinclude monofluoroethylene, difluoroethylenes, trifluoroethylene,tetrafluoroethylene, monochloroethylene, dichloroethylenes,trichloroethylene, tetrachloroethylene, and the like. Also, alkynes suchas acetylene (C₂H₂), propyne (C₃H₄), butyne (C₄H₆), vinylacetylene andderivatives thereof can be used as carbon precursors. Additionallycyclic hydrocarbons, such as benzene, styrene, toluene, xylene,ethylbenzene, acetophenone, methyl benzoate, phenyl acetate,phenylacetylene (C₈H₆), phenol, cresol, furan, alpha-terpinene, cymene,1,1,3,3,-tetramethylbutylbenzene, t-butylether, t-butylethylene,methyl-methacrylate, and t-butylfurfurylether, compounds having theformula C₃H₂ and C₅H₄, halogenated aromatic compounds includingmonofluorobenzene, difluorobenzenes, tetrafluorobenzenes,hexafluorobenzene and the like can be used. Halogenated hydrocarbonssuch as carbon tetrachloride (CCl₄), diiodomethane (CH₂I₂),chlorofluorocarbon (CFC), bromotrichloromethane (BrCCl₃),1,1-dichloroethylene, bromobenzene, or derivatives thereof may also beused.

Examples of suitable derivatives of hydrocarbon compounds may include,but not limited to fluorinated alkanes, halogenated alkanes, andhalogenated aromatic compounds. Fluorinated alkanes may include, but notlimited to monofluoromethane, difluoromethane, trifluoromethane,tetrafluoromethane, monofluoroethane, tetrafluoroethanes,pentafluoroethane, hexafluoroethane, monofluoropropanes,trifluoropropanes, pentafluoropropanes, perfluoropropane,monofluorobutanes, trifluorobutanes, tetrafluorobutanes,octafluorobutanes, difluorobutanes, monofluoropentanes,pentafluoropentanes, tetrafluorohexanes, tetrafluoroheptanes,hexafluoroheptanes, difluorooctanes, pentafluorooctanes,difluorotetrafluorooctanes, monofluorononanes, hexafluorononanes,difluorodecanes, pentafluorodecanes, and the like. Halogenated alkenesmay include, but not limited to monofluoroethylene, difluoroethylenes,trifluoroethylene, tetrafluoroethylene, monochloroethylene,dichloroethylenes, trichloroethylene, tetrachloroethylene, and the like.Halogenated aromatic compounds may include, but not limited tomonofluorobenzene, difluorobenzenes, tetrafluorobenzenes,hexafluorobenzene and the like.

Nitrogen-containing hydrocarbon compounds or derivatives thereof thatmay be included in the nitrogen-containing hydrocarbon source can bedescribed by the formula CxHyNz, where x has a range of between 1 and12, y has a range of between 2 and 20, and z has a range of between 1and 10. Suitable nitrogen containing hydrocarbon compounds may includeone or more of the following compounds methylamine, dimethylamine,trimethylamine (TMA), triethylamine, quinoline, imidiazole, vinylimidazole, acetonitrile, acrilonitrile, aniline, pyrrole, pyridine,piperidine, and benzonitrile.

In certain embodiments, oxygen-containing hydrocarbons compounds such asbenzaldehyde, acetophenone, anisole, diethyl ether, acetone, metanol,ethanol, isopropanol, ethanolamine, cresol, morpholine, or divinyl ethermay also be used in the deposition of amorphous carbon film.

The plasma-initiating gas may be introduced into the PECVD chamber atbefore and/or same time as the hydrocarbon compound and a plasma isinitiated to begin deposition. The plasma-initiating gas may be a highionization potential gas including, and not limited to, helium gas,hydrogen gas, nitrogen gas, argon gas and combinations thereof. Theplasma-initiating gas may also be a chemically inert gas, such as heliumgas, nitrogen gas, or argon gas. Suitable ionization potentials forgases are from about 5 eV (electron potential) to 25 eV. Theplasma-initiating gas may be introduced into the PECVD chamber prior tothe nitrogen containing hydrocarbon source and/or the hydrocarbonsource, which allows a stable plasma to be formed and reduces thechances of arcing.

An inert gas is typically used as a dilution gas or a carrier gas toflow with the hydrocarbon source, the plasma-initiating gas, thenitrogen containing hydrocarbon source, or combinations thereof.Suitable dilution gases may include argon (Ar), helium (He), hydrogen(H₂), nitrogen (N₂), ammonia (NH₃), noble gas such as krypton, xenon, orany combinations thereof. In one example, argon is used as the dilutiongas for reasons of economy. Ar, He, and N₂ may be used to control thedensity and deposition rate of the amorphous carbon layer. In somecases, the addition of H₂ and/or NH₃ can be used to control the hydrogenratio of the amorphous carbon layer. In cases where alkynes such asacetylene (C₂H₂) or alkenes such as propylene is used as hydrocarbonsource, the carrier gas may not be used during the deposition.

Conformality of amorphous carbon can be enhanced by choice of precursorsand deposition conditions. In general, precursors with lower H:C ratio(<1:1 ratio) yield higher conformality. Exemplary process conditions fordeposition of a conformal amorphous carbon film are described below.

A hydrocarbon source, a nitrogen-containing gas and a dilution gas maybe introduced into a PECVD chamber to deposit a nitrogen-doped amorphouscarbon. The hydrocarbon source may be any suitable hydrocarbon compoundas discussed above. If a liquid hydrocarbon source is used, theprecursor flow may be between about 50 mg/min to about 1000 mg/min. If agaseous hydrocarbon source is used, the precursor flow may be betweenabout 100 sccm to about 5000 sccm, for example about 200 sccm to about600 sccm. If a carrier gas is used, the carrier flow may be betweenabout 500 sccm and about 10000 sccm. The plasma-initiating gas may beany suitable plasma-initiating gas as discussed above, and flowed at aflow rate from about 0 sccm to about 50,000 sccm, for example, betweenabout 400 sccm to about 8,000 sccm. The dilution gas may be any dilutiongas as described above and supplied at a flow rate from about 0 sccm toabout 5,000 sccm, for example about 500 sccm to about 1,000 sccm. Theflow rate described herein is intended for a 300 mm substrate, which mayvary depending upon the size of the substrate.

In various embodiments, the nitrogen-containing gas may be introduced ata nitrogen-containing gas to hydrocarbon source ratio of about 1:100 toabout 20:1, for example about 1:40 to about 10:1. The dilution gas maybe introduced at a dilution gas to hydrocarbon source ratio of about 2:1to about 40:1, for example about 20:1 to about 30:1. In one embodiment,a volumetric flow rate of hydrocarbon source:nitrogen-containinggas:plasma-initiating gas:dilution gas is in a ratio of, for exampleabout 1:1:0.5:20, for example about 1:0.5:0.5:20, for example about1:0.2:0.5:20, for example about 1:0.2:0.5:30, for example about1:0.2:0.5:40.

If a nitrogen-containing hydrocarbon source (as described above) isused, the nitrogen-containing hydrocarbon gas may be flowed at a flowrate from about 10 sccm to about 2,000 sccm, for example, from about 500sccm to about 1,500 sccm. In case the nitrogen-containing hydrocarbonsource is a liquid precursor, the nitrogen-containing hydrocarbon sourceflow can be between 15 mg/min and 2,000 mg/min, for example between 100mg/min and 1,000 mg/min. In one embodiment, a volumetric flow rate ofnitrogen-containing hydrocarbon source: the plasma-initiatinggas:dilution gas is in a ratio of, for example about 1:0.5:20, forexample about 1:0.2:20, for example about 1:0.8:20, for example about1:1:20, for example about 1:0.5:30, for example about 1:0.5:40.

During the deposition, the substrate temperature may be maintainedbetween about 0° C. to about 250° C., for example between about 25° C.and about 150° C., such as between 25° C. and 75° C., in order tominimize damage to previously formed features or layers. The processchamber may be maintained at a chamber pressure about 100 mTorr to about100 Torr, for example from about 2 Torr to about 15 Torr, for exampleabout 8 Torr or greater, such as about 20 Torr. Plasma may be generatedby applying RF power at a power density to substrate surface area offrom about 0.001 W/cm² to about 5 W/cm², such as from about 0.01 W/cm²to about 1 W/cm², for example about 0.04 W/cm² to about 0.07 W/cm². Thepower application may be from about 1 Watt to about 2,000 watts, such asfrom about 10 W to about 100 W, for a 300 mm substrate. RF power can beeither single frequency or dual frequency. A dual frequency RF powerapplication is believed to provide independent control of flux and ionenergy since the energy of the ions hitting the film surface influencesthe film density. The applied RF power and use of one or morefrequencies may be varied based upon the substrate size and theequipment used. If a single frequency power is used, the frequency powermay be between about 10 KHz and about 30 MHz, for example about 13.56MHz or greater, such as 27 MHz or 60 MHz. If a dual-frequency RF poweris used to generate the plasma, a mixed RF power may be used. The mixedRF power may provide a high frequency power in a range from about 10 MHzto about 60 MHz, for example, about 13.56 MHz, 27 MHz or 60 MHz, as wellas a low frequency power in a range of from about 10 KHz to about 1 MHz,for example, about 350 KHz. Electrode spacing, i.e., the distancebetween a substrate and a showerhead, may be from about 200 mils toabout 1000 mils, for example, from about 280 mils to about 300 milsspacing.

The process range as discussed herein provides a deposition rate for anitrogen doped amorphous carbon layer in the range of about 10 Å/min toabout 30,000 Å/min. One skilled in the art, upon reading the disclosureherein, can calculate appropriate process parameters in order to producea nitrogen doped amorphous carbon film of different deposition rates.The as-deposited nitrogen-doped amorphous carbon layer has an adjustablecarbon:nitrogen ratio that ranges from about 0.1% nitrogen to about 10%nitrogen, such as about 2% to about 6%. An example of nitrogen dopedamorphous carbon materials deposited by the processes described hereinis provided as follows.

As discussed above, at suitable conditions, the energetic plasma,comprising some combination of carbon, nitrogen and hydrogen atoms,reacts with and binds to the surface of patterned photoresist layer 202to form a conformal organic layer 218. The conformal organic layer 218grows uniformly over the surface of the photoresist layer 202, and isphysically and chemically adhered to the soft carbon surface ofphotoresist layer 202. Advantageously, it is believed that the lowtemperature of deposition and low thermal energy of the photoresistsurface lessens desorption of the energetic impinging carbon, nitrogenand hydrogen atoms, thus leading to greater sticking and binding of theatoms to the soft carbon photoresist surface. Not to be restricted bytheory, the chemical bonding of the conformal carbon film to surface ofthe carbonaceous photoresist may be realized by carbon-carbon bonding,and carbon-nitrogen bonding. The plasma processes performed herein maycreate unsatisfied chemical valence and dangling bonds in atoms at thesubstrate surface, such as a carbon containing photoresist. At thesurface, the carbon dangling bonds combine with energetic carbonradicals to form new chemical bonds.

The low temperature methods typically yield higher growth rates ofconformal organic layer 218 and lower intrinsic carbon layer stresses.By comparison, higher temperature deposits of carbon feature higherstresses due to increased cross-linking, shrinkage, and differences indensity, which may lead to delamination of the carbon layer 218 anddistortion of the photoresist layer 202. Further unexpected advantagesin some embodiments are realized by judicious choice of hydrocarbon andnitrogen precursors. For example, propylene and ammonia may producecarbon layers with enhanced adhesion to the photoresist, step coverageand other desirable carbon layer properties. In one example, propylenegas and ammonia gas are introduced into a processing chamber at avolumetric hydrocarbon source and nitrogen source volumetric ratio ofbetween about 50:1 and about 5:1, and wherein the plasma is generated inthe processing chamber is delivered at an RF power density between about0.01 W/cm² and about 10 W/cm².

Next, the conformal organic layer 218 is removed using an anisotropicetch process, at 106 and as illustrated in FIG. 2D. Here the layer 218is removed from the top field region and the bottom of the feature usinga plasma etching process. In some embodiments, the selective etchingprocess may be an anisotropic etching process designed to etch materialfrom horizontal surfaces of the substrate only. Such processes mayfeature a plasma etchant with an electrical bias applied to thesubstrate to encourage ions in the plasma to accelerate toward thesubstrate surface, and thus remove the conformal organic layer 218 fromthe bottom as shown in FIG. 2D. At the same time, such a process mayalso result in substantial removal of the conformal organic layer 218from the field region of the photoresist layer 202, also illustrated inFIG. 2D. Reactive ion etching using fluorine and oxygen ions is oneexample of a selective etching process useful for practicing embodimentsof the disclosure. Other suitable etching methods, such as etching bynon-reactive ions, may also be used.

The pattern transfer hardmask layer 204 may be a hardmask layer derivedfrom a physical vapor deposition process (PVD), and may be comprised ofsilicon oxide or silicon rich oxide, or PVD SiN or silicon rich SiN, orSiC or silicon rich SiC, or a combination of the preceding including avariation which includes controlled doping of hydrogen into thecompounds, heretofore referred to as the hardmask layer orSiO_(w)N_(x):H_(y), where w, x, y, each can vary in concentration from0% to 100%. In one embodiment, w has a range of between 1 and 50, x hasa range of between 0 and 50, y has a range of 0 to 50.

The pattern transfer hardmask layer 204 will serve as an etch mask forsubsequent etch sequences, and may be a dielectric layer,anti-reflective layer, or barrier layer, and may possess more than onesuch property.

The hardmask layer 204 is produced as a hardmask with optical propertiesthat are sufficiently matched to a photoresist layer 202. Opticalproperties such as index of refraction (n) and extinction coefficient(k) of hardmask layer 204 are matched to the photoresist layer 202, sothat the interface of the photoresist layer 202 and hardmask layer 204does not produce reflections that compromise the lithographic patterningprocess. In some embodiments, matching the optical properties of thehardmask and the photoresist allows for multiple sequences of litho,etch, photoresist strip and reapplication of photoresist to be performeddirectly on the hardmask layer 204. Moreover, since the material fromwhich the hardmask layer 204 is formed is unaffected by the subsequentplasma assisted ashing process that is used to remove the photoresistlayer 202 and conformal organic layer 218 layers, and thus allow thesubsequent litho, etch, photoresist strip and reapplication ofphotoresist process cycles to be performed as many times as required tofrom a desirable pattern in the hardmask layer 204. In one embodimentthe photoresist layer 202 and the hardmask layer 204 has a refractiveindex (n) equal to between 1.6 and 1.7 and an extinction coefficient (k)equal to 0.00 and 0.12 at a wavelength of 193 nm, such as 0.05. As aresult, the exposure electromagnetic energy will not reflect or refractat the physical interface of the hardmask layer 204 and the overlyingphotoresist layer 202.

One example of a PVD process chamber (e.g., a sputter process chamber)that may be adapted for and suitable for sputter depositing the Hardmasklayer 204, is an Impulse™ Pulsed DC PVD Dielectric Chamber, availablefrom Applied Materials, Inc., located in Santa Clara, Calif. It iscontemplated that other sputter process chambers, including those fromother manufactures, may be adapted to practice the present disclosure.

The deposition of a conformal organic layer 218, the removal of theconformal organic layer 218 and the etching of the exposed portiondescribed in 104, 106 and/or 108 may be repeated one or more times, at110. Of note, 104 may be repeated alone, 104 and 106 may be repeated insequence; 104, 106 and 108 may be repeated in sequence; or combinationsthereof. In one example, a total of four (4) cycles are completed. Thefirst cycle consisting of 104 and 106; the second cycle consisting of104, the third cycle consisting of 104, 106 and 108 and the fourth cycleconsisting of 104 and 106. Further varieties of combinations areenvisioned.

As illustrated by FIG. 2E, an optional second conformal organic layer220 is deposited over or on the field region, sidewalls, and the bottomportion formed by the patterned photoresist layer 202, the conformalorganic layer 218 and the upper surface of the reduced dimension patterntransfer hardmask layer 204. The second conformal organic layer 220 maybe disposed over or on the conformal organic layer 218 and the patternedphotoresist layer 202 by a PECVD process from gaseous precursors thatare provided to a reactor containing the multilayer substrate 200.Suitable process chambers, gases used in the deposition process andprocess parameters may be substantially the same as described above withreference to FIG. 2C. It is contemplated that other processing systems,including those available from other manufacturers, may be adapted topractice the embodiments described herein.

The second conformal organic layer 220, when deposited using processconditions discussed below, will achieve step coverage of at least about80% or more, for example about 100% or more, such as 120%. The thicknessof the second conformal organic layer 220 may be between about 5 Å andabout 200 Å. In one embodiment, the second conformal organic layer 220has the same composition as the conformal organic layer 218. In oneexample, the second conformal organic layer 220 is a nitrogen-dopedcarbon layer. The second conformal organic layer 220 is deposited usinga deposition gas, which includes at least a hydrocarbon source. Thehydrocarbon source used for the second conformal organic layer 220 maybe selected from possible sources described with reference to FIG. 2C.

The hydrocarbon source may be a mixture of one or more hydrocarboncompounds. The hydrocarbon source may include a gas-phase hydrocarboncompound and/or a gas mixture including vapors of a liquid-phasehydrocarbon compound and a carrier gas, as described with reference toFIG. 2C. The deposition gas can be initiated using a plasma-initiatinggas. The plasma-initiating gas may be helium since it is easily ionized;however, other gases, such as argon, may also be used. The dilution gasmay be an easily ionized, relatively massive, and chemically inert gassuch as argon, krypton, xenon. In some cases, additional hydrogendilution can be introduced to further increase the film density, as willbe discussed later.

The plasma-initiating gas may be introduced into the PECVD chamber atbefore and/or same time as the hydrocarbon compound and a plasma isinitiated to begin deposition. The plasma-initiating gas may be a highionization potential gas including, and not limited to, helium gas,hydrogen gas, nitrogen gas, argon gas and combinations thereof. Theplasma-initiating gas may also be a chemically inert gas, such as heliumgas, nitrogen gas, or argon gas. Suitable ionization potentials forgases are from about 5 eV (electron potential) to 25 eV. Theplasma-initiating gas may be introduced into the PECVD chamber prior tothe nitrogen containing hydrocarbon source and/or the hydrocarbonsource, which allows a stable plasma to be formed and reduces thechances of arcing.

An inert gas is typically used as a dilution gas or a carrier gas toflow with the hydrocarbon source, the plasma-initiating gas, thenitrogen containing hydrocarbon source, or combinations thereof.Suitable dilution gases and parameters thereof can be the same asdilution gases described with reference to FIG. 2C. Conformality ofamorphous carbon can be optimized by choice of precursors and depositionconditions. In general, precursors with lower H:C ratio (<1:1 ratio)yield higher conformality.

As discussed above, at suitable conditions, the energetic plasma,comprising some combination of carbon, nitrogen and hydrogen atoms,reacts with and binds to the surface of patterned photoresist layer 202and to the surface of the conformal organic layer 218 to form a secondconformal organic layer 220. The second conformal organic layer 220grows uniformly over the surface of the photoresist layer 202 and theconformal organic layer 218, and is physically and chemically adhered tothe surfaces thereof. By depositing a second conformal organic layer220, the CD of the features is further reduced without changing thethickness of the photoresist layer 202.

The low temperature methods typically yield higher growth rates ofsecond conformal organic layer 220 and lower intrinsic carbon layerstresses. By comparison, higher temperature deposits of carbon featurehigher stresses due to increased cross-linking, shrinkage, anddifferences in density, which may lead to delamination of the secondconformal organic layer 220 and distortion of the photoresist layer 202.Further unexpected advantages in some embodiments are realized byjudicious choice of hydrocarbon and nitrogen precursors. For example,propylene and ammonia may produce carbon layers with enhanced adhesionto the photoresist, step coverage and other desirable carbon layerproperties. In one example, propylene gas and ammonia gas are introducedinto a processing chamber at a volumetric hydrocarbon source andnitrogen source volumetric ratio of between about 50:1 and about 5:1,and wherein the plasma is generated in the processing chamber isdelivered at an RF power density between about 0.01 W/cm² and about 10W/cm². Different chemistries may be chosen for better adherence to theconformal organic layer 218.

Next, the second conformal organic layer 220 is removed using ananisotropic etch process, as illustrated in FIG. 2F. Here the secondconformal organic layer 220 is removed from the top field region and thebottom of the feature using a plasma etching process. In someembodiments, the selective etching process may be an anisotropic etchingprocess designed to etch material from horizontal surfaces of thesubstrate only. Such processes may be substantially similar to theprocesses described with reference to removing the conformal organiclayer 218 from the bottom as described with reference to FIGS. 2C and2D. At the same time, such a process may also result in substantialremoval of the second conformal organic layer 220 from the field regionof the photoresist layer 202, also illustrated in FIG. 2D. Reactive ionetching using fluorine and oxygen ions is one example of a selectiveetching process useful for practicing embodiments of the disclosure.Other suitable etching methods, such as etching by non-reactive ions,may also be used.

As illustrated in FIG. 2G, the conformal organic layer 218 and thesecond conformal organic layer 220 deposited on the sidewalls serves asan etching mask for creation of a reduced dimension feature in thehardmask layer 204, at 108. The thickness of the conformal organic layer218 and the second conformal organic layer 220 on the sidewalls definethe critical dimension of the pattern etched into hardmask layer 204.For example, if the recess or pattern originally formed in thephotoresist is 40 nm wide, a conformal organic layer 218 which is 5 nmwide on opposite sidewalls and a second conformal organic layer 220which is 5 nm wide on opposite sidewalls will reduce the width of thepattern etched in the hardmask layer 204 to 20 nm after a directional oranisotropic etch. If the second conformal organic layer 220 is formedfrom a material having high etch selectivity with respect to the etchantused to etch the hardmask layer 204, the second conformal organic layer220 will only etch slowly or not at all, leaving a reduced criticaldimension feature etched in the hardmask layer 204 as shown in FIG. 2E.Etching of the hardmask layer 204 may be performed by any method knownto etch the material of which the hardmask layer 204 is formed. In oneembodiment, the etch is performed by a process that will notsignificantly etch the conformal organic layer 218 or the secondconformal organic layer 220. A directional etch, such as etching underbias using reactive or non-reactive ions, may be advantageous forpreserving the sidewall remnants of the second conformal organic layer220 while etching the reduced dimension pattern in the hardmask layer204. The directional selective etching process may be a directional oranisotropic etching process designed to etch material from horizontalsurfaces of the substrate only. Such processes may feature a plasmaetchant with an electrical bias applied to the substrate to encourageions in the plasma to accelerate toward the substrate surface. In suchprocesses, the accelerated ions will generally travel deep into thepattern recess such that a vast majority of reactive species impact thebottom portion of the recess as shown in FIGS. 2F and 2G. Reactive ionetching using fluorine and oxygen ions is one example of a selectiveetching process useful for practicing embodiments of the disclosure.Other etching methods, such as etching by non-reactive ions, may also beused.

Multiple steps are performed to achieve the reduced dimension in theactive layer 214 disposed over substrate 216 in FIG. 2H. Layer 214 maybe described as the active layer comprised of reduced dimension linesand vias that are patterned in a dielectric material. As describedherein, the method 100 may be useful in generating patterns havingcritical dimension smaller than the capability of a particularlithography apparatus or process.

Embodiments described herein relate to deposition of an ultra-conformalcarbon-based material for decreasing the critical dimensions and lineedge roughness of a feature formed in a photoresist or a hardmask. Bydepositing a conformal organic layer over formed features, prior toetching a component layer of a device, the size of the etched featurecan be reduced, in some cases beyond the minimum etch size which isoptically producible by the device. Further, the conformal organic layerwill smooth out the roughness of the sidewall of the etched photoresist.Thus, the resulting feature will be both smaller and have reducedimperfections as compared to features formed by other methods.

While the foregoing is directed to embodiments of the methods anddevices described herein, other and further embodiments may be devisedwithout departing from the basic scope thereof, and the scope thereof isdetermined by the claims that follow.

The invention claimed is:
 1. A method of processing a substrate,comprising: forming a feature in a photoresist layer to expose a portionof a hardmask layer deposited below the photoresist layer; depositing afirst organic layer directly on the photoresist layer, the first organiclayer conformally covering exposed surfaces of the feature and exposedportions of the hardmask layer; selectively removing the first organiclayer from a top surface of the photoresist layer and the exposedportions of the hardmask layer, while leaving the first organic layerdeposited on sidewalls of the feature substantially intact; forming asecond organic layer conformally on the top surface of the photoresistlayer, the exposed portion of the hardmask layer and the sidewalls ofthe feature; selectively removing the second organic layer from the topsurface of the photoresist layer and the exposed portion of the hardmasklayer, while leaving the second organic layer deposited on the firstorganic layer on the sidewalls of the feature substantially intact; andforming a pattern into the hardmask layer using the photoresist layer,the first organic layer and the second organic layer as a mask.
 2. Themethod of claim 1, wherein the forming a pattern into the hardmask layerexposes a portion of an anti-reflective layer deposited below thehardmask layer.
 3. The method of claim 1, further comprising: removingthe first organic layer and the second organic layer and the photoresistlayer.
 4. The method of claim 1, wherein the thickness of the firstorganic layer and the thickness of the second organic layer on thesidewalls define a critical dimension of the pattern formed into thehardmask layer.
 5. The method of claim 1, wherein the forming a patterninto the hardmask layer is performed by a directional etch or ananisotropic etch process with an electrical bias applied to thesubstrate.
 6. The method of claim 5, wherein the directional etch or theanisotropic etch process uses fluorine and oxygen ions.
 7. The method ofclaim 1, wherein the deposition of the first organic layer is maintainedat a temperature of between about 25° C. and about 150° C.
 8. A methodof processing a substrate, comprising: forming a feature in aphotoresist layer to expose a portion of a hardmask layer depositedbelow the photoresist layer; depositing a first organic layer directlyon the photoresist layer by exposing the photoresist layer to a plasmaformed from a hydrocarbon source, a plasma-initiating gas, and adilution gas, the first organic layer conformally covering exposedsurfaces of the feature and exposed portions of the hardmask layer;selectively removing the first organic layer from a top surface of thephotoresist layer and the exposed portions of the hardmask layer, whileleaving the first organic layer deposited on sidewalls of the featuresubstantially intact; forming a second organic layer conformally on thetop surface of the photoresist layer, the exposed portion of thehardmask layer and the sidewalls of the feature; selectively removingthe second organic layer from the top surface of the photoresist layerand the exposed portion of the hardmask layer, while leaving the secondorganic layer deposited on the first organic layer on the sidewalls ofthe feature substantially intact; and forming a pattern into thehardmask layer using the photoresist layer, the first organic layer andthe second organic layer as a mask.
 9. The method of claim 8, whereinthe hydrocarbon source is a nitrogen-containing hydrocarbon sourcecomprising methylamine, dimethylamine, trimethylamine (TMA),triethylamine, aniline, quinoline, pyridine, acrilonitrile,benzonitrile, or combinations thereof.
 10. The method of claim 8,wherein the hydrocarbon source comprises a fluorine-containing gas, anoxygen-containing gas, a hydroxyl group-containing gas, and aboron-containing gas.
 11. The method of claim 10, wherein thehydrocarbon source further comprises a nitrogen-containing gas.
 12. Themethod of claim 11, wherein the hydrocarbon source comprises alkynes oralkenes.
 13. The method of claim 12, wherein the hydrocarbon sourcecomprises acetylene (C₂H₂) or propylene.
 14. The method of claim 13,wherein the hydrocarbon source is propylene and the nitrogen-containinggas is ammonia.
 15. The method of claim 14, wherein the hydrocarbonsource is introduced into a processing chamber at a first volumetricflowrate and the nitrogen-containing gas is introduced into theprocessing chamber at a second volumetric flowrate, and a ratio of thefirst volumetric flowrate to the second volumetric flowrate is betweenabout 50:1 and about 5:1.
 16. The method of claim 8, wherein thedeposition of the first organic layer is maintained at a temperature ofbetween about 25° C. and about 150° C.
 17. A method of processing asubstrate, comprising: forming a feature in a photoresist layer toexpose a portion of a hardmask layer deposited below the photoresistlayer; depositing a first organic layer directly on the photoresistlayer, wherein the first organic layer is an amorphous carbon layerconformally covering exposed surfaces of the feature and exposedportions of the hardmask layer; selectively removing the first organiclayer from a top surface of the photoresist layer and the exposedportions of the hardmask layer, while leaving the first organic layerdeposited on sidewalls of the feature substantially intact; forming asecond organic layer conformally on the top surface of the photoresistlayer, wherein the second organic layer is an amorphous carbon layer;selectively removing the second organic layer from the top surface ofthe photoresist layer and the exposed portion of the hardmask layer,while leaving the second organic layer deposited on the first organiclayer on the sidewalls of the feature substantially intact; and forminga pattern into the hardmask layer using the photoresist layer, the firstorganic layer and the second organic layer as a mask.
 18. The method ofclaim 17, wherein the deposition of the first organic layer ismaintained at a temperature of between about 25° C. and about 150° C.19. The method of claim 17, wherein the depositing a first organic layerdirectly on the photoresist layer is performed by exposing thephotoresist layer to a plasma formed from a nitrogen-containinghydrocarbon source, a plasma-initiating gas, and a dilution gas.
 20. Themethod of claim 19, wherein the nitrogen-containing hydrocarbon sourcecomprises methylamine, dimethylamine, trimethylamine (TMA),triethylamine, aniline, quinoline, pyridine, acrilonitrile,benzonitrile, or combinations thereof.